// Issue 1147 https://github.com/typetools/checker-framework/issues/1147

import java.util.StringJoiner;

public class Issue1147 {

  public static void main(String[] args) {

    StringJoiner sj = new StringJoiner(",");

    sj.add("a");

    sj.add(null);

    System.out.println(sj);
  }
}